Can you share some tech jargon how you have implemented network stuff.

Sure, basically all the networking is handled by the wonderful Kryonet library. I also use the Kryo library to serialize the messages sent between the client and the server.

Player movement is controlled by the mouse, so for example I have a class MousePosition which sends the current mouse coordinates from the client to the server. The server will then receive this information and move the player in those coordinates direction.

Originally I was making the game sideways like you mentioned, and for the exact same reason (I have a 1600x900 resolution). I changed it to top down because I thought this was the preference for most players. But my plan is to give the option for sure.

What do you mean exactly by buying half of the game? Feel free to pm me your ideas.